The present invention relates to an optical fiber
receptacle and a method of producing the same. More specifically, it relates to an optical fiber receptacle used in a terminal for an optical communication subscriber such as a home, an office, or a factory and for optically connecting an optical fiber to a light-emitting element or a light-receiving element, and particularly relates to an optical fiber receptacle in which a glass rod lens fixed in its inside and an optical fiber are aligned certainly, and a method of producing the same.
Optical communication has been popularized rapidly in recent years so as to be utilized in personal use for telephones, facsimiles and so on, and also in mass-media for television information and so on. In order to connect a signal from an optical fiber as an optical signal transmission medium to a home telephone or the like, a terminal device is set. In the terminal device, the optical fiber is optically connected to a light-receiving element for reception and to a light-emitting element for transmission. The light-receiving element and the light-emitting element perform conversion between an electric signal and an optical signal.
A schematic view of a structure considered as the structure of the aforementioned terminal device at the present time is shown in FIG. 9. In FIG. 9, reference numeral 52 designates an optical fiber receptacle which is formed so that a glass rod lens 51 is provided at one end side thereof and a connector of an optical fiber 53 is to be connected to the other end side by a push-on type joining method or the like. A light-emitting element 54 and a light-receiving element 55 are arranged in the front of the glass rod lens 51 through a half mirror 56 so as to be connected respectively efficiently. The whole of those parts is covered with a casing 57. Examples of the optical fiber used include a single mode fiber and a multi-mode fiber. The single mode fiber has a very small core diameter of from 9 to 10 .mu.m and the multi-mode fiber has also a very small core diameter of about 50 .mu.m. In order to connect the light-emitting element 54 and the light-receiving element 55 to the optical fiber efficiently, as shown in FIG. 9, the optical fiber is once connected to the glass rod lens 51 before the glass rod lens 51 is connected to the light-emitting element 54 and to the light-receiving element 55. An optical fiber receptacle is used as a simple connector for connecting the optical fiber to the glass rod lens.
In the conventional optical fiber receptacle, the glass rod lens having an outside diameter equal to the outside diameter of a ferrule having a center hole in which the optical fiber is inserted and protected, is inserted and fixed into a cylindrical sleeve having an inside diameter substantially equal to the outside diameters of the ferrule and the glass rod lens, and then the ferrule of a front end portion of the optical fiber is inserted into the sleeve to thereby bring the optical fiber into physical contact with the glass rod lens.
As another structure, a glass rod lens holder is produced with high mechanical accuracy with respect to a ferrule holder, and the holders are fitted and welded after the ferrule and the glass rod lens are inserted into the holders respectively with high accuracy.
A commonly used ferrule for a multi-mode optical fiber has an outside diameter of 2.499 mm .+-.0.001 mm or from 2.499 mm -0.002 mm to 2.499 mm +0.001 mm. A commonly used ferrule for a single mode optical fiber has an outside diameter of 2.499 mm .+-.0.0005 mm. As the refractive index of the glass lens, a refractive index near the refractive index (1.452 in the case of a quartz fiber) of the optical fiber core is selected.
The outside diametrical portion of the glass rod lens must be machined and polished with the same accuracy as that of the ferrule in order to insert the glass rod lens into the same and one sleeve while making the center axis of the glass rod lens coincident with the center axis of the ferrule. However, it is very difficult to machine and polish the glass rod lens with the same accuracy as that of the ferrule.
Further, in the case where an end of a cylinder is polished spherically in mechanical machining or the like, it is generally impossible that the center of the spherical surface thus spherically polished is made perfectly coincident with the center axis (the center axis of the outside diametrical portion of the cylindrical glass lens) of the cylinder. As a result, eccentricity is produced. Thus, there arises a problem that coupling of the eccentric glass lens and the optical fiber becomes unstable to cause an increase in reflection loss even in the case where the eccentricity produced is slight. Even in the case where the high accuracy machining method in the present circumstances is used, the accuracy of the outside diametrical portion and the eccentric accuracy are respectively limited to the order of tens of .mu.m. In a try and error state, the eccentricity of about 50 .mu.m is produced as the eccentricity of the abutment surface due to the aforementioned accuracy. There also arises a problem that there is no simple and accurate method to reduce the eccentricity through adjustment.